Americanmuscle.com sells tuners for a relatively good price. Granted it still expensive, but whenever you buy a tuner you automatically get enrolled in their "Free Tunes for Life" program which does the following: you get three tunes from the get-go, one for daily driving, one for performance, and one for all-out racing. All you do is send them your Mustang's specifications and other things you wish to include. The best part is that after that if you do anymore mods to your Mustang, you can get all three tunes redone for free. The downside is that you don't get the tunes written on a dyno, but you get them done right away and then if you want more just take the tunes to the dyno and optimize them.
2014 Ford Focus ST (ST3, Tuxedo Black Metallic)
1985 Chevrolet C10 Custom Deluxe (Red)
2003 Ford Mustang GT Centennial Edition (Black) (SOLD)
2004 Ford Mustang GT (Redfire) (SOLD)
1997 Ford Mustang GT (Rio Red) (SOLD)